1. Field of the Invention
The present invention relates to a system for displaying images, and more particularly to, a device and a method of driving a light source for image display devices and an image display device having the same.
2. Description of the Related Art
Image display devices, such as computer monitors, television sets, etc., generally include self-emitting display devices and non- emitting display devices. The self-emitting display devices are ones that actively emit light themselves to display images, such as light emitting diode (LED) display devices, electroluminescence (EL) display devices, vacuum fluorescent display (VFD) devices, field emission display (FED) devices, and plasma panel display (PDP) devices. In contrast, the non-emitting display devices are ones that use light externally provided from a light source, such as liquid crystal display (LCD) devices.
The LCD devices generally include two panels having electric field generating electrodes and a liquid crystal layer having dielectric anisotropy, which is interposed between the two panels. In an LCD device, the electric field generating electrodes receive electric voltages and generate electric field across the liquid crystal layer. Light transmittance of the liquid crystal layer varies depending on the strength of the electric field applied thereto, and the electric field is controlled by the voltages applied to the electric field generating electrodes. Desired images are displayed by adjusting the applied voltages.
The LCD devices employ either natural light or light generated from a light source, such as lamps, that is equipped in the LCD devices. When an LCD device employs lamps as the light source, the brightness on a screen of the LCD device is usually adjusted by regulating the ratio of on and off durations of the lamps or regulating the current flowing in the lamps.
The lamps for the LCD devices usually include fluorescent lamps. The fluorescent lamps generally require a high AC voltage having a magnitude typically in the range of several kilovolts and a frequency typically in the range of dozens of kilohertz. The current flowing in such fluorescent lamps has a magnitude of several milli-amperes.
Since the lamps in an LCD device are closely disposed at the rear side of an LCD panel at a distance of several millimeters, electric and/or magnetic fields generated from the lamps make noise to signals in wires and thin film transistors (TFTs) of the LCD panel. In particular, since the frequency of a driving signal for the lamps and the frequency of a horizontal synchronization signal for the LCD panel are similar but slightly different from each other, a beating occurs to cause interference that makes horizontal stripes, called “waterfall,” on a screen of the LCD device.